Superabsorbent particles containing carboxyalkyl cellulose and temporary metal crosslinks

ABSTRACT

Particles comprising a combination of a carboxyalkyl cellulose and a galactomannan polymer or a glucomannan polymer, wherein the particles comprise a plurality of non-permanent metal crosslinks.

BACKGROUND OF THE INVENTION

Personal care absorbent products, such as infant diapers, adultincontinent pads, and feminine care products, typically contain anabsorbent core that includes superabsorbent polymer particlesdistributed within a fibrous matrix. Superabsorbents arewater-swellable, generally water-insoluble absorbent materials having ahigh absorbent capacity for body fluids. Superabsorbent polymers (SAPs)in common use are mostly derived from acrylic acid, which is itselfderived from petroleum oil, a non-renewable raw material. Acrylic acidpolymers and SAPs are generally recognized as not being biodegradable.Despite their wide use, some segments of the absorbent products marketare concerned about the use of non-renewable petroleum oil derivedmaterials and their non-biodegradable nature. Acrylic acid basedpolymers also comprise a meaningful portion of the cost structure ofdiapers and incontinent pads. Users of SAP are interested in lower costSAPs. The high cost derives in part from the cost structure for themanufacture of acrylic acid which, in turn, depends upon the fluctuatingprice of petroleum oil. Also, when diapers are discarded after use theynormally contain considerably less than their maximum or theoreticalcontent of body fluids. In other words, in terms of their fluid holdingcapacity, they are “over-designed”. This “over-design” constitutes aninefficiency in the use of SAP. The inefficiency results in part fromthe fact that SAPs are designed to have high gel strength (asdemonstrated by high absorbency under load or AUL). The high gelstrength (upon swelling) of currently used SAP particles helps them toretain a lot of void space between particles, which is helpful for rapidfluid uptake. However, this high “void volume” simultaneously results inthere being a lot of interstitial (between particle) liquid in theproduct in the saturated state. When there is a lot of interstitialliquid the “rewet” value or “wet feeling” of an absorbent product iscompromised.

In personal care absorbent products, U.S. southern pine fluff pulp iscommonly used in conjunction with the SAP. This fluff is recognizedworldwide as the preferred fiber for absorbent products. The preferenceis based on the fluff pulp's advantageous high fiber length (about 2.8mm) and its relative ease of processing from a wetland pulp sheet to anairlaid web. Fluff pulp is also made from renewable and biodegradablecellulose pulp fibers. Compared to SAP, these fibers are inexpensive ona per mass basis, but tend to be more expensive on a per unit of liquidheld basis. These fluff pulp fibers mostly absorb within the intersticesbetween fibers. For this reason, a fibrous matrix readily releasesacquired liquid on application of pressure. The tendency to releaseacquired liquid can result in significant skin wetness during use of anabsorbent product that includes a core formed exclusively fromcellulosic fibers. Such products also tend to leak acquired liquidbecause liquid is not effectively retained in such a fibrous absorbentcore.

Superabsorbent composite particles prepared from renewable naturalpolymers have advantages over superabsorbent particles obtained frompetroleum oil based synthetic polymers in lower cost, biodegradabilityand being derived from renewable natural polymers. As such there is aneed for new superabsorbent compositions derived from renewable naturalpolymers.

A need therefore exists for a composite superabsorbent material that issimultaneously derived from biodegradable renewable resources likecellulose and that is inexpensive. In this way, the superabsorbentmaterial can be used in absorbent product designs that are efficient.These and other objectives are accomplished by the invention set forthbelow.

SUMMARY OF THE INVENTION

The invention provides superabsorbent particles that includecarboxyalkyl cellulose. The particles include a combination of acarboxyalkyl cellulose and a galactomannan polymer or a glucomannanpolymer, and a plurality of non-permanent metal crosslinks.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present invention provides superabsorbent particlesthat contain carboxyalkyl cellulose. The particles include a combinationof a carboxyalkyl cellulose and a galactomannan polymer or a glucomannanpolymer, and a plurality of non-permanent metal crosslinks.

The particles include a carboxyalkyl cellulose. Suitable carboxyalkylcelluloses have a degree of carboxyl group substitution of from about0.3 to about 2.5, and in one embodiment have a degree of carboxyl groupsubstitution of from about 0.5 to about 1.5. In one embodiment, thecarboxyalkyl cellulose is carboxymethyl cellulose. The particles includefrom about 60 to about 99% by weight carboxyalkyl cellulose based on thetotal weight of carboxyalkyl cellulose and galactomannan or glucomannanpolymer. In one embodiment, the particles include from about 80 to about95% by weight carboxyalkyl cellulose based on the total weight ofcarboxyalkyl cellulose and galactomannan or glucomannan polymer.

The particles include a galactomannan polymer or a glucomannan polymer.Suitable galactomannan polymers include guar gum, locust bean gum, andtara gum. Suitable glucomannan polymers include konjac gum. Thegalactomannan polymer or glucomannan polymer can be from natural sourcesor obtained from genetically-modified plants. The particles include fromabout 1 to about 20% by weight galactomannan polymer or glucomannanpolymer based on the total weight of the carboxyalkyl cellulose andgalactomannan or glucomannan polymer, and in one embodiment, theparticles include from about 1 to about 15% by weight galactomannanpolymer or glucomannan polymer based on the total weight of thecarboxyalkyl cellulose and galactomannan or glucomannan polymer.

The particles are substantially insoluble in water while being capableof absorbing water. The particles are rendered water insoluble by aplurality of non-permanent interpolymer metal crosslinks.

The particles have intermolecular metal crosslinks between polymermolecules. The metal crosslink arises as a consequence of an associativeinteraction (e.g., bonding) between functional groups on the polymers(e.g., carboxy, carboxylate, or hydroxyl groups) and a multi-valentmetal species. Suitable multi-valent metal species include metal ionshaving a valency of three or greater and that are capable of forming anassociative interaction with a polymer (e.g., reactive towardassociative interaction with the polymer's carboxy, carboxylate, orhydroxyl groups). The polymers are intermolecularly crosslinked when themulti-valent metal species forms an associative interaction withfunctional groups on two or more polymer molecules. A crosslink may beformed within one polymer molecule or may be formed between two or morepolymer molecules. The extent of crosslinking affects the watersolubility of the particles and the ability of the particles to swell oncontact with an aqueous liquid.

The particles include non-permanent metal crosslinks formed bothintermolecularly and intramolecularly in the population of polymermolecules. As used herein, the term “non-permanent crosslink” refers tothe metal crosslink formed with two or more functional groups of apolymer molecule (intramolecularly) or formed with two or morefunctional groups of two or more polymer molecules (intermolecularly).It will be appreciated that the process of dissociating andre-associating (breaking and reforming crosslinks) the multi-valentmetal ion and polymer molecules is dynamic and also occurs during liquidacquisition. During water acquisition the individual particles swell andchange to gel state. The ability of non-permanent metal crosslinks todissociate and associate under water acquisition imparts greater freedomto the gels to expand than if it was restrictively crosslinked bypermanent crosslinks that do not have the ability to dissociate andreassociate. Covalent organic crosslinks such as ether crosslinks arepermanent crosslinks that do not have the ability to dissociate andreassociate.

The crosslinks are formed by treating the carboxyalkyl cellulose andgalactomannan or glucomannan polymer with a crosslinking agent. Suitablecrosslinking agents include crosslinking agents that are reactivetowards hydroxyl groups and carboxyl groups. Representative crosslinkingagents include metallic crosslinking agents, such as aluminum (III)compounds, titanium (IV) compounds, bismuth (III) compounds, boron (III)compounds, and zirconium (IV) compounds. The numerals in parentheses inthe preceding list of metallic crosslinking agents refers to the valencyof the metal.

Representative metallic crosslinking agents include aluminum sulfate;aluminum hydroxide; dihydroxy aluminum acetate (stabilized with boricacid); other aluminum salts of carboxylic acids and inorganic acids;other aluminum complexes, such as Ultrion 8186 from Nalco Company(aluminum chloride hydroxide); boric acid; sodium metaborate; ammoniumzirconium carbonate (AZC); zirconium compounds containing inorganic ionsorganic ions or neutral ligands; bismuth ammonium citrate (BAC); otherbismuth salts of carboxylic acids and inorganic acids; titanium (IV)compounds, such as titanium (IV) bis(triethylaminato) bis(isopropoxide)(commercially available from the Dupont Company under the designationTyzor TE); and other titanates with alkoxide or carboxylate ligands.

The crosslinking agent is effective for intermolecularly crosslinkingthe carboxyalkyl cellulose (with or without carboxyalkyl hemicellulose)and galactomannan polymer or glucomannan polymer molecules. Thecrosslinking agent is applied in an amount of from about 0.1 to about20% by weight based on the total weight of the carboxyalkyl celluloseand galactomannan or glucomannan polymers. The amount of crosslinkingagent applied to the polymers will vary depending on the crosslinkingagent. In general, the particles have an aluminum content of about 0.04to about 2.0% by weight based on the weight of the particles foraluminum crosslinked particles, a titanium content of about 0.1 to about4.5% by weight based on the weight of the particles for titaniumcrosslinked particles, a zirconium content of about 0.09 to about 6.0%by weight based on the weight of the particles for zirconium crosslinkedparticles; and a bismuth content of about 0.09 to about 5.0% by weightbased on the weight of the particles for bismuth crosslinked particles.

The particles are highly absorptive. The particles have a Free SwellCapacity of from about 30 to about 60 g/g (0.9% saline solution), aCentrifuge Retention Capacity (CRC) of from about 15 to about 35 g/g(0.9% saline solution), and an Absorbency Under Load (AUL) of from about15 to about 30 g/g (0.9% saline solution).

The particles are water insoluble and water swellable. Waterinsolubility is imparted by intermolecular crosslinking of the polymermolecules, and water swellability is imparted to the absorbent particlesby the presence of carboxylate anions with associated cations. Theparticles are characterized as having a relatively high liquid absorbentcapacity for water (e.g., pure water or aqueous solutions, such as saltsolutions or biological solutions such as urine).

The particles are useful as a superabsorbent composition in personalcare absorbent products (e.g., infant diapers, feminine care productsand adult incontinence products). The particles are useful in a varietyof other applications, including, for example, wound dressings, cablewrap, absorbent sheets or bags, and packaging materials.

The preparations of representative superabsorbent particles aredescribed in Examples 1-6. In these examples solutions of arepresentative carboxyalkyl cellulose and a galactomannan polymer arecrosslinked with a metallic crosslinking agent. The composition andliquid absorbent characteristics of representative superabsorbentparticles (flakes) are summarized in Table 1. In Table 1, “% wgt totalwgt, applied” refers to the amount of crosslinking agent applied to thetotal weight of CMC and guar gum; “CMC 9H4F” refers to a carboxymethylcellulose commercially available from Hoechst Celanese under thatdesignation; “PA-CMC” refers to CMC made from northern softwood pulp;“LB Gum” refers to locust bean gum; and “AZC” refers to ammoniumzirconium carbonate.

The superabsorbent particles containing carboxyalkyl cellulose can bemade by a method that includes the steps of (a) blending a carboxyalkylcellulose and either a galactomannan polymer or a glucomannan polymer inwater to provide an aqueous solution; (b) treating the aqueous solutionwith a first crosslinking agent to provide a gel; (c) drying the gel toprovide a solid; and (d) comminuting the solid to provide a plurality ofparticles.

In the process, a carboxyalkyl cellulose and either a galactomannanpolymer or a glucomannan polymer are blended in water to provide anaqueous solution. In one embodiment, the carboxyalkyl cellulose iscarboxymethyl cellulose. The aqueous solution includes from about 60 toabout 99% by weight carboxyalkyl cellulose based on the weight ofcarboxyalkyl cellulose and galactomannan or glucomannan polymers. In oneembodiment, the aqueous solution includes from about 80 to about 95% byweight carboxyalkyl cellulose based on the weight of carboxyalkylcellulose and galactomannan or glucomannan polymers.

The aqueous solution also includes a galactomannan polymer or aglucomannan polymer. The aqueous solution includes from about 1 to about20% by weight galactomannan polymer or glucomannan polymer based on theweight of the carboxyalkyl cellulose and galactomannan or glucomannanpolymers, and in one embodiment, the aqueous solution includes fromabout 1 to about 15% by weight galactomannan polymer or glucomannanpolymer based on the weight of the carboxyalkyl cellulose andgalactomannan or glucomannan polymers.

In the method, the aqueous solution including the carboxyalkyl celluloseand galactomannan polymer or glucomannan polymer is treated with acrosslinking agent to provide a gel. Suitable crosslinking agents aredescribed above. The crosslinking agent is applied in an amount of fromabout 0.1 to about 20% by weight based on the total weight of thecarboxyalkyl cellulose and galactomannan or glucomannan polymers. Theamount of crosslinking agent applied to the polymers will vary dependingon the crosslinking agent.

The gel formed by treating the aqueous solution of a carboxyalkylcellulose and a galactomannan polymer or glucomannan polymer with thecrosslinking agent is then dried to provide a solid that is thencomminuted to provide a plurality of particles (superabsorbentparticles). In one embodiment, the particles are sieved to obtainparticles having a size of from about 150 to about 800 μm. In oneembodiment, the particles have a size less than about 800 μm.

Test Methods Free Swell and Centrifuge Retention Capacities

The materials, procedure, and calculations to determine free swellcapacity (g/g) and centrifuge retention capacity (CRC) (g/g) were asfollows.

Test Materials:

Japanese pre-made empty tea bags (available from Drugstore.com, INPURSUIT OF TEA polyester tea bags 93 mm×70 mm with fold-over flap.(http:www.mesh.ne.jp/tokiwa/).

Balance (4 decimal place accuracy, 0.0001 g for air-dried superabsorbentpolymer (ADS SAP) and tea bag weights); timer; 1% saline; drip rack withclips (NLM 211); and lab centrifuge (NLM 211, Spin-X spin extractor,model 776S, 3,300 RPM, 120 v).

Test Procedure:

1. Determine solids content of ADS.

2. Pre-weigh tea bags to nearest 0.0001 g and record.

3. Accurately weigh 0.2025 g+/−0.0025 g of test material (SAP), recordand place into pre-weighed tea bag (air-dried (AD) bag weight). (ADSweight+AD bag weight=total dry weight).

4. Fold tea bag edge over closing bag.

5. Fill a container (at least 3 inches deep) with at least 2 inches with1% saline.

6. Hold tea bag (with test sample) flat and shake to distribute testmaterial evenly through bag.

7. Lay tea bag onto surface of saline and start timer.

8. Soak bags for specified time (e.g., 30 minutes).

9. Remove tea bags carefully, being careful not to spill any contentsfrom bags, hang from a clip on drip rack for 3 minutes.

10. Carefully remove each bag, weigh, and record (drip weight).

11. Place tea bags onto centrifuge walls, being careful not to let themtouch and careful to balance evenly around wall.

12. Lock down lid and start timer. Spin for 75 seconds.

13. Unlock lid and remove bags. Weigh each bag and record weight(centrifuge weight).

Calculations:

The tea bag material has an absorbency determined as follows:

Free Swell Capacity, factor=5.78

Centrifuge Capacity, factor=0.50

Z=Oven dry SAP wt (g)/Air dry SAP wt (g)

Free Capacity (g/g):

$\frac{\begin{matrix}{\left\lbrack {\left( {{{drip}\mspace{14mu}{wt}\mspace{11mu}(g)} - {{dry}\mspace{14mu}{bag}\mspace{14mu}{wt}\mspace{11mu}(g)}} \right) - \left( {{AD}\mspace{14mu}{SAP}\mspace{14mu}{wt}\mspace{11mu}(g)} \right)} \right\rbrack -} \\\left( {{dry}\mspace{14mu}{bag}\mspace{14mu}{wt}\mspace{11mu}(g)*5.78} \right)\end{matrix}}{\left( {{AD}\mspace{14mu}{SAP}\mspace{14mu}{wt}\mspace{11mu}(g)*Z} \right)}$

Centrifuge Retention Capacity (g/g):

$\frac{\begin{matrix}{\left\lbrack {{{centrifuge}\mspace{14mu}{wt}\mspace{11mu}(g)} - {{dry}\mspace{14mu}{bag}\mspace{14mu}{wt}\mspace{11mu}(g)} - \left( {{AD}\mspace{14mu}{SAP}\mspace{14mu}{wt}\mspace{11mu}(g)} \right)} \right\rbrack -} \\\left( {{dry}\mspace{14mu}{bag}\mspace{14mu}{wt}\mspace{11mu}(g)*0.50} \right)\end{matrix}}{\left( {{AD}\mspace{14mu}{SAP}\mspace{14mu}{wt}*Z} \right)}$

Absorbency Under Load (AUL)

The materials, procedure, and calculations to determine AUL were asfollows.

Test Materials:

Mettler Toledo PB 3002 balance and BALANCE-LINK software or othercompatible balance and software. Software set-up: record weight frombalance every 30 sec (this will be a negative number. Software can placeeach value into EXCEL spreadsheet.

Kontes 90 mm ULTRA-WARE filter set up with fritted glass (coarse) filterplate. clamped to stand; 2 L glass bottle with outlet tube near bottomof bottle; rubber stopper with glass tube through the stopper that fitsthe bottle (air inlet); TYGON tubing; stainless steel rod/plexiglassplunger assembly (71 mm diameter); stainless steel weight with holedrill through to place over plunger (plunger and weight=867 g); VWR 9.0cm filter papers (Qualitative 413 catalog number 28310-048) cut down to80 mm size; double-stick SCOTCH tape; and 0.9% saline.

Test Procedure:

1. Level filter set-up with small level.

2. Adjust filter height or fluid level in bottle so that fritted glassfilter and saline level in bottle are at same height.

3. Make sure that there are no kinks in tubing or air bubbles in tubingor under fritted glass filter plate.

4. Place filter paper into filter and place stainless steel weight ontofilter paper.

5. Wait for 5-10 min while filter paper becomes fully wetted and reachesequilibrium with applied weight.

6. Zero balance.

7. While waiting for filter paper to reach equilibrium prepare plungerwith double stick tape on bottom.

8. Place plunger (with tape) onto separate scale and zero scale.

9. Place plunger into dry test material so that a monolayer of materialis stuck to the bottom by the double stick tape.

10. Weigh the plunger and test material on zeroed scale and recordweight of dry test material (dry material weight 0.15 g+/−0.05 g).

11. Filter paper should be at equilibrium by now, zero scale.

12. Start balance recording software.

13. Remove weight and place plunger and test material into filterassembly.

14. Place weight onto plunger assembly.

15. Wait for test to complete (30 or 60 min)

16. Stop balance recording software.

Calculations:

-   -   A=balance reading (g)*−1 (weight of saline absorbed by test        material)    -   B=dry weight of test material (this can be corrected for        moisture by multiplying the AD weight by solids %).        AUL(g/g)=A/B(g 1% saline/1 g test material)

The following examples are provided for the purpose of illustrating, notlimiting, the invention.

EXAMPLES Example 1 The Preparation of Representative SuperabsorbentParticles (Flakes): Ammonium Zirconium Carbonate and Boric AcidCrosslinking

In this example, the preparation of representative superabsorbentcomposite crosslinked with ammonium zirconium carbonate is described.

Prepare a solution of CMC 9H4F 10.0 g OD in 900 ml deionized water withvigorous stirring to obtain a smooth solution. Fully dissolve 0.6 g guargum in 50 ml DI water and mix well with the CMC solution. Mix thesolution for further one hour to allow complete mixing of the twopolymers.

Blend the polymer mixture in the blender for 5 minutes. Fully dissolveboric acid 0.1 g in 30 ml DI water. Dilute 2.0 g ammonium zirconiumcarbonate solution (15% ZrO₂) with 20 ml DI water. Transfer ammoniumzirconium carbonate solution and boric acid solution to the polymersolution and blend for 5 minutes. Pour the gel into a Teflon coated panand dry in the oven at 60° C. Grind the dry film in a coffee grinder andsieve. Collect 300-800 μm fraction for testing.

T-bag test for free swell 45.87 g/g; centrifuge capacity 26.11 g/g; andAUL 26.57 g/g (at 0.3 psi) for 0.9% saline solution.

Example 2 The Preparation of Representative Superabsorbent Particles(Flakes): Aluminum Sulfate/Boric Acid Crosslinking

In this example, the preparation of representative superabsorbentcomposite crosslinked with aluminum sulfate and boric acid is described.

Prepare a solution of CMC 9H4F 10.0 g OD in 900 ml deionized water withvigorous stirring to obtain a solution. Dissolve 0.6 g guar gum in 50 mlDI water and mix well with the CMC solution. Mix the solution forfurther one hour to allow complete mixing of the two polymers.

Blend the polymer mixture in the blender for 5 minutes. Fully dissolveboric acid 0.1 g in 30 ml DI water. Dissolve 0.4 g aluminum sulfateoctadecahydrate 20 ml DI water. Transfer boric acid solution andaluminum sulfate solution to the polymer solution and blend for 5minutes to mix well. Pour the gel into a Teflon coated pan and dry inthe oven at 60° C. Grind the dry film in a coffee grinder and sieve.Collect 300-800 μm fraction for testing.

T-bag test for free swell 46.83 g/g; centrifuge capacity 27.35 g/g; andAUL 29.13 g/g (at 0.3 psi) for 0.9% saline solution.

Example 3 The Preparation of Representative Superabsorbent Particles(Flakes): Tyzor TE and Boric Acid Crosslinking

In this example, the preparation of representative superabsorbentcomposite crosslinked with Tyzor TE and boric acid is described.

Prepare a solution of CMC 9H4F 10.0 g OD in 900 ml deionized water withvigorous stirring to obtain a smooth solution. Dissolve 0.6 g guar gumin 50 ml DI water and mix well with the CMC solution. Mix the solutionfor further one hour to allow complete mixing of the two polymers.

Blend the polymer mixture in the blender for 5 minutes. Dissolve boricacid 0.2 g in 30 ml DI water. Dilute 0.2 g Tyzor TE with 20 ml DI water.Transfer Tyzor TE solution and boric acid solution to the polymersolution and blend for 5 minutes to mix well. Pour the gel into a Tefloncoated pan and dry in the oven at 60° C. Grind the dry film in a coffeegrinder and sieve. Collect 300-800 μm fraction for testing.

T-bag test for free swell 43.92 g/g; centrifuge capacity 24.46 g/g; andAUL 23.17 g/g (at 0.3 psi.) for 0.9 saline solution.

Example 4 The Preparation of Representative Superabsorbent Particles(Flakes): Aluminum Sulfate and Boric Acid Crosslinking

In this example, the preparation of representative superabsorbentcomposite crosslinked with aluminum sulfate and boric acid is described.

Prepare a solution of CMC 9H4F 10.0 g OD in 900 ml deionized water withvigorous stirring to obtain a solution. Dissolve 0.6 g locust bean gumin 50 ml DI water and mix well with the CMC solution. Mix the solutionfor further one hour to allow complete mixing of the two polymers.

Blend the polymer mixture in the blender for 5 minutes. Dissolve boricacid 0.1 g in 30 ml DI water. Dissolve 0.6 g aluminum sulfateoctadecahydrate in 20 ml DI water. Transfer boric acid solution andaluminum sulfate solution to the polymer solution and blend for 5minutes to mix well. Pour the gel into a Teflon coated pan and dry inthe oven at 60° C. Grind the dry film in a coffee grinder and sieve.Collect 300-800 μm fraction for testing.

T-bag test for free swell 44.62 g/g; centrifuge capacity 25.09 g/g; andAUL 27.66 g/g (at 0.3 psi) for 0.9% saline.

Example 5 The Preparation of Representative Superabsorbent Particles(Flakes): Ammonium Zirconium Carbonate and Boric Acid Crosslinking

In this example, the preparation of representative superabsorbentcomposite crosslinked with ammonium zirconium carbonate is described.

Prepare a solution of CMC 9H4F 10.0 g OD (11.1 g) in 900 ml deionizedwater with vigorous stirring to obtain a solution. Dissolve 0.6 g locustbean gum in 50 ml DI water and mix well with the CMC solution. Mix thesolution for one hour to allow complete mixing of the two polymers.

Blend the polymer mixture in the blender for 5 minutes. Dissolve boricacid 0.1 g in 30 ml DI water. Dilute 2.0 g ammonium zirconium carbonatesolution (15% ZrO₂) with 20 ml DI water. Transfer ammonium zirconiumcarbonate and boric acid solution to the polymer solution and blend for5 minutes to mix well. Pour the gel into a Teflon coated pan and dry inthe oven at 60° C. Grind the dry film in a coffee grinder and sieve.Collect 300-800 μm fraction for testing.

T-bag test for free swell 35.58 g/g; centrifuge capacity 19.56 g/g; andAUL 28.8 g/g (at 0.3 psi) for 0.9% saline solution.

Example 6 The Preparation of Representative Superabsorbent Particles(Flakes): Aluminum Acetate and Boric Acid Crosslinking

In this example, the preparation of representative superabsorbentcomposite crosslinked with aluminum acetate and boric acid is described.

Prepare a solution of CMC 9H4F 40.0 g OD in 3600 ml deionized water withvigorous stirring to obtain a solution. Dissolve 2.4 g guar gum in 350ml DI water and mix well with the CMC solution. Mix the solution for onehour to allow complete mixing of the two polymers.

Dissolve 0.15 g aluminum acetate/boric acid (Aldrich) in 50 ml water.Transfer aluminum acetate/boric acid solution to the polymer solutionand blend for 5 minutes to mix well. Pour the gel into a Teflon coatedpan and dry in the oven at 60° C. Grind the dry film in a coffee grinderand sieve. Collect 300-800 μm fraction for testing.

T-bag test for free swell 86.79 g/g; centrifuge capacity 65.85 g/g; andAUL 27.66 g/g (at 0.3 psi) for 0.9% saline solution.

In Table 1, A1 acetate/boric acid is dihydroxy aluminum acetate•⅓ boricacid from Aldrich Chemical Co.

TABLE 1 Superabsorbent Flakes From Crosslinked Aqueous Mixtures of CMCand Galactomannans Galactomannan Crosslinking agent Free Swell CRC AULSample CMC (wgt % total wgt) (wgt % total wgt, applied) (g/g) (g/g)(g/g) 1 CMC 9H4F Guar Gum 5.5% (AZC) Zr 1.38%, Na₂B₄O₇ 0.9% 73.28 33.7523.26 2 CMC 9H4F Guar Gum 5.4% (AZC) Zr 2.72%, Na₂B₄O₇ 0.9% 51.57 33.4224.95 3 CMC 9H4F Guar Gum 5.4% (AZC) Zr 4.0%, Na₂B₄O₇ 0.9% 37.07 19.9525.86 4 CMC 9H4F Guar Gum 5.3% (AZC) Zr 5.3% 25.79 11.1 21.93 5 CMC 9H4FGuar Gum 5.5% (AZC) Zr 1.36%, B(OH)₃ 1.8% 60.02 41.41 27.4 6 CMC 9H4FGuar Gum 5.4% (AZC) Zr 1.35%, B(OH)₃ 2.7% 64.29 45.82 27.04 7 CMC 9H4FGuar Gum 5.4% (AZC) Zr 2.72%, B(OH)₃ 0.9% 45.87 26.11 26.57 8 CMC 9H4FGuar Gum 5.5% (AZC) Zr 2.75% 47.79 28.92 27.13 9 CMC 9H4F Guar Gum 5.4%Al₂(SO₄)₃ 2.72%, B(OH)₃ 0.9% 43.81 23.08 28.02 10 CMC 9H4F Guar Gum 5.4%Al₂(SO₄)₃ 1.83%, B(OH)₃ 0.9% 46.83 27.35 29.13 11 CMC 9H4F Guar Gum 5.4%Al₂(SO₄)₃ 0.9%, B(OH)₃ 0.9% 64.36 51.18 27.51 12 CMC 9H4F Guar Gum 5.4%Al₂(SO₄)₃ 2.75% 50 32.81 23.62 13 CMC 9H4F Guar Gum 5.3% Al₂(SO₄)₃ 2.6%,Tyzor TE 4.2% 43.92 24.46 23.17 14 CMC 9H4F Guar Gum 5.8% Al₂(SO₄)₃1.8%, Tyzor TE 4.2% 55.58 24.46 26.4 15 CMC 9H4F Guar Gum 5.9% Al₂(SO₄)₃1.0%, Tyzor TE 4.3% 72.93 39.47 25.4 16 CMC 9H4F Guar Gum 5.1% Al₂(SO₄)₃2.5%, Tyzor TE 6.8% 46.71 52.01 22.62 17 CMC 9H4F LB Gum 5.4% Al₂(SO₄)₃2.72%, B(OH)₃ 0.9% 44.62 25.09 27.66 18 CMC 9H4F LB Gum 5.4% Al₂(SO₄)₃1.83%, B(OH)₃ 0.9% 46.15 28.28 27.57 19 CMC 9H4F LB Gum 5.4% Al₂(SO₄)₃0.9%, B(OH)₃ 0.9% 54.91 37.93 29.13 20 CMC 9H4F LB Gum 5.4% Al₂(SO₄)₃2.75% 47.12 27.72 28.26 21 CMC 9H4F LB Gum 5.4% (AZC) Zr 1.36%, B(OH)₃1.8% 52.13 35.37 31.88 22 CMC 9H4F LB Gum 5.4% (AZC) Zr 1.35%, B(OH)₃2.7% 53.64 36.59 31.15 23 CMC 9H4F LB Gum 5.4% (AZC) Zr 2.72%, B(OH)₃0.9% 35.58 19.56 28.8 24 CMC 9H4F LB Gum 5.4% (AZC) Zr 2.75% 37.59 19.7428.91 25 CMC 9H4F LB Gum 5.4% (AZC) Zr 2% 44.79 26.6 26.6 26 CMC 9H4F LBGum 5.4% Al Acetate/Boric acid 2% 36.41 18.33 26.66 27 CMC 9H4F LB Gum5.4% Al Acetate/Boric acid 3% 30.36 13.57 26.06 28 CMC 9H4F LB Gum 5.4%Al Acetate/Boric acid 5% 30.17 12.74 23.46 29 CMC 9H4F LB Gum 5.4% AlAcetate/Boric acid 0.25% 70.12 54.1 31.46 30 CMC 9H4F LB Gum 5.4% AlAcetate/Boric acid 0.5% 57.96 40.74 29.37 31 CMC 9H4F LB Gum 5.4% AlAcetate/Boric acid 1% 50.24 29.48 30.24 32 CMC 9H4F LB Gum 5.4% AlAcetate/Boric acid 1.5% NS 43.73 24.23 27.55 33 PA-CMC Guar Gum 5.4%Al₂(SO₄)₃ 2.72%, B(OH)₃ 0.9% 32.74 14.43 29.44 34 PA-CMC Guar Gum 5.4%Al₂(SO₄)₃ 1.83%, B(OH)₃ 0.9% 39.84 19.44 27.64 35 PA-CMC Guar Gum 5.4%Al₂(SO₄)₃ 0.9%, B(OH)₃ 0.9% 49 30.12 25.73 36 PA-CMC Guar Gum 5.4%Al₂(SO₄)₃ 2.75% 41.5 22.72 26.08 37 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃2.72%, B(OH)₃ 0.9% 29.33 11.64 30.91 38 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃1.83%, B(OH)₃ 0.9% 32.14 13.29 27.44 39 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃0.9%, B(OH)₃ 0.9% 35.41 13.81 26 40 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 2.75%36.5 13.96 30.42 41 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 2.72%, B(OH)₃ 0.9%33.21 13.65 27.66 42 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 1.83%, B(OH)₃ 0.9%36.21 16.43 28.13 43 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 0.9%, B(OH)₃ 0.9%47.45 26.51 27.06 44 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 2.75% 41.12 19.0828.02 45 PA-CMC Guar Gum 5.5% (AZC) Zr 1.0%, B(OH)₃ 0.9% 61.36 46.4826.82 46 PA-CMC Guar Gum 5.5% (AZC) Zr 1.5%, B(OH)₃ 0.9% 58.7 43.0824.84 47 PA-CMC Guar Gum 5.5% (AZC) Zr 2.0%, B(OH)₃ 0.9% 58.48 41.2128.68 48 PA-CMC Guar Gum 5.5% (AZC) Zr 2.5%, B(OH)₃ 0.9% 40.26 23.8325.95 49 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 2.72%, B(OH)₃ 0.9% 64.35 49.8125.8 50 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 1.83%, B(OH)₃ 0.9% 68.85 54.4824.06 51 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 0.9%, B(OH)₃ 0.9% 75.38 56.3522.86 52 PA-CMC Guar Gum 5.4% Al₂(SO₄)₃ 2.75% 50.54 33.92 26.35

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

1. Particles comprising a combination of a carboxyalkyl cellulose and agalactomannan polymer or a glucomannan polymer, wherein the particlescomprise a plurality of non-permanent metal crosslinks and wherein theparticles do not have permanent crosslinks.
 2. The particles of claim 1,wherein the carboxyalkyl cellulose has a degree of carboxyl groupsubstitution of from about 0.3 to about 2.5.
 3. The particles of claim1, wherein the carboxyalkyl cellulose is carboxymethyl cellulose.
 4. Theparticles of claim 1, wherein the galactomannan polymer is selected fromthe group consisting of guar gum, locust bean gum, and tarn gum.
 5. Theparticles of claim 1, wherein the glucomannan polymer is konjac gum. 6.The particles of claim 1, wherein the galactomannan polymer orglucomannan polymer is present in an amount from about 1 to about 20percent by weight based on the total weight of the particles.
 7. Theparticles of claim 1, wherein the carboxyalkyl cellulose is present inan amount from about 60 to about 99 percent based on the total weight ofparticles.
 8. The particles of claim 1, wherein the non-permanent metalcrosslinks comprise multi-valent metal ion crosslinks.
 9. The particlesof claim 1, wherein the non-permanent metal crosslinks comprise one ormore metal ions selected from the group consisting of aluminum, boron,bismuth, titanium, and zirconium, and mixtures thereof.
 10. Theparticles of claim 1 having a free swell capacity of from about 30 toabout 60 g/g for 0.9% saline solution.
 11. The particles of claim 1having a centrifuge retention capacity of from about 15 to about 35 g/gfor 0.9% saline solution.
 12. The particles of claim 1 having anabsorbency under load capacity of from about 15 to about 30 g/g for 0.9%saline solution.
 13. The particles of claim 1 having a size less thanabout 800 μm.